1. Field of Invention
The present invention relates to a mobile terminal device or other mobile communication device having a plurality of antennas, and to an antenna switch for switching the connection between a plurality of antennas and a reception circuit in a mobile terminal device or other mobile communication device.
2. Description of the Related Art
For example, as a high speed wireless communication system for mobile terminal devices such as mobile phones, in recent years the code division multiple access (CDMA) 2000 1x-EVDO system (hereinafter abbreviated as the “EVDO system”) has been developed. The “EVDO system” is standardized in Standard (Specification) T64 IS-2000 C.G. 0024 “High Rate Packet Data Air Interface Specification” of the Association of Radio Industries and Business (ARIB) and is designed to further raise the data rate in data communication for the CDMA2000 1X system (hereinafter abbreviated as the “1x system”).
In the “EVDO system”, an uplink communication wireless interface for transmission from a mobile terminal device to a base station uses a quadrature phase shift keying (QPSK) as a modulation scheme and uses a CDMA as the multiplex scheme. Its configuration is substantially equivalent to the “1x system”. In the “EVDO system”, however, the downlink communication wireless interface for transmission from the base station to the mobile terminal device differs from the “1x system”. Namely, for the modulation scheme of downlink communication of the “EVDO system”, either of the QPSK, an 8-position quadrature phase shift keying (8 PSK), or a 16-position phase amplitude modulation (16 QAM) is used in response to the reception conditions of the mobile terminal device, while for the multiplex scheme, not CDMA, but the time division multiplex access (TDMA) scheme is used.
In the TDMA scheme, time is divided into a plurality of unit times, each of 1/600 second. A base station communicates with only one mobile terminal device in a divided unit time (time slot) and communicates with a plurality of mobile terminal devices by switching the mobile terminal devices communicated with by time. Therefore, in the unit time, it becomes possible to communicate data for each individual mobile terminal device using the maximum power. Data can be communicated between the mobile terminal devices via the base station at a high speed. In the TDMA scheme, unlike personal digital cellular (PDC) phone and other communication devices, the base station side methodically determines (schedules) the mobile terminal devices that communicates with for each unit time slot.
A variety of improved technologies are being developed for mobile terminal devices of the “EVDO system” described above. For example, Japanese Patent Publication (Kokai) No. 2002-369247-A discloses a technology relating to assignment of unit time slots for efficiently using the transmission ability of the base station, while Japanese Patent Publication (Kokai) No. 2002-344560-A discloses technology optimizing the data error rate and communication speed in a downlink data communication.
Further, Japanese Patent Publication (Kokai) No. 2004-32443-A discloses technology providing a detachable external antenna in addition to an ordinary transmission/reception antenna and switching the ordinary antenna and the external antenna in accordance with the reception conditions for a diversity reception. The “diversity reception” scheme is technology eliminating the influence of phasing and improving the reception conditions. The diversity reception (antenna diversity) selects for example the reception signal of the antenna providing the strongest reception strength among the signals received from a plurality of antennas or sequentially selects reception signals of antennas providing high reception strengths and combines these reception signals (selection/combination to thereby enable a mobile terminal device communicating in a reception environment in which phasing occurs to obtain a reception signal having a high signal strength and receive the reception signal in a preferred state in that environment.
The detachable external antenna disclosed in Japanese Patent Publication (Kokai) No. 2004-32443-A is used for improving the reception enviroment when a mobile terminal device is positioned inside a building and the reception conditions of the wireless signal are bad. In that case, the external antenna is positioned at a location in the building where tho reception environment is good, for example, at a window side. By the user connecting a cable of the external antenna to a corresponding terminal (attachment portion) of the mobile terminal device if required and utilizing the reception signal of the external antenna, the reception conditions of the mobile terminal device are improved.
As described above, in order to realize a diversity reception in a mobile terminal device, sometimes a plurality of antennas are required, for example, at least one additional antenna is provided in addition to the ordinary transmission/reception antenna, while a further antenna becomes necessary for extended functions. For example, as an antenna for extended functions, there is for example an antenna receiving a signal from a global positioning system (GPS) satellite for acquiring positioning information.
In a mobile terminal device provided with a plurality of antennas such as two transmission/reception antennas enabling a diversity reception and a GPS antenna, an antenna switch for efficiently switching the reception signals received from the plurality of antennas and outputting them to the reception circuit, GPS processing circuit, or other later signal processing circuit in accordance with the reception environment, the state of attachment or an external antenna, and so on is demanded. The above example was described with reference to a mobile phone or other mobile terminal device as the mobile communication device, but the same is true for other mobile communication devices having a plurality of antennas for realizing diversity reception and extended functions.